On Sun, 22 Jul 2007, Igor Stoppa wrote:
Hi,
On Sat, 2007-07-21 at 23:49 -0700, ext
[email protected] wrote:
I'm deliberatly breaking the threading on this so that people who have
tuned out the hibernation thread can take a look at this.
below is the proposal that I made at the bottom of one of the posts on the
hibernation thread.
I have the impression that you are trying to describe a mix of the clock
and latency frameworks.
Could you elaborate on how your proposal is incompatible with enhancing
the clock framework?
It's not that I think it's incompatible with any existing powersaving
tools (in fact I hope it's not)
it's that I think that this (or something similar) could be made to cover
all thevarious power options instead of CPU's having one interface, ACPI
capable drivers having another, embeded devices presenting a third, etc
this was triggered by the mess of different function calls for different
purposes that are used for the suspend functions where you have a bunch of
different functions that are each supposed to be called at a specific time
from a specific mode during the suspend process. with all these different
functions driver writes tend to not bother implementing any of them, and
it seems like there is a fairly steady stream of new functions that end up
being needed. the initial intent was to just change this into a generic
set of calls that every driver writer would implement the minimum set of,
and make it trivially extensable to future capabilities of hardware.
one other effect of this is that driver writers would see the mode
interface from day one rather then just completely ignoring it. right now
device driver authors tend to thing " why worry about figuring out how to
implement 'prepare to suspend', 'late suspend', 'suspend', 'quiese but
don't suspend', etc" if they aren't really interested in working on
suspend, it's not really clear what each of these should do even after
reading the docs on it. however listing the power modes that a device can
be in, documenting the cost of switching between them, and implementing
the transition is something very straightforward for the device driver
author to do (and they don't have to worry about the details of how and
when the various modes get used, that's up to the suspend/powersaving
software to figure out). as such I expect that the driver support for
powersaving modes to improve. in fact, I expect that some driver writers
will implement a whole bunch of modes, just to show off the features of
the hardware. and even if nothing uses the modes right now at least they
are implemented and documented for future use (and it should be trivial to
have a test routine that just runs every driver you have hardware for
through every mode transition to make sure that they all work, so the less
commonly used modes shouldn't bitrot too badly)
while I was describing the issues to my roomates over dinner I realized
that the same type of functions are needed for the CPU clocks.
if you have an accepted framework in place there that can do what I
described, please consider extending it to cover other types of devices
and drivers.
I want sanity and functionality far more then credit :-)
David Lang
It looks like you are proposing a brand new shiny thing that frankly I
would be happy to leave alone, unless it is crystal clear that the clock
fw cannot be improved.
The clocfk fw is used for OMAP and other architectures (including SH,
iirc) and so far it has provided very good support for our power
management needs (Nokia 770 and N800).
Currently we are working on DVFS for OMAP2 (see slides presented at the
linux-pm summit for OLS 2007 http://tinyurl.com/28tact ) and even if the
current prototype is not actively involving the clock fw, our final goal
is to make it capable of supporting atomic transactions for changing the
core parameters.
thanks for the link. I've read through it, and it looks like there is a
lot of the same ideas in your proposal. I think you are passing too much
info up the chain to the part makeing the decision (that part doesn't need
to know the details of the voltage/freq choices, the %power/%capability
numbers I suggested are in many ways more what they are making decision
son anyway)
in the slideshow you list in the sequence of changing the cpu speed to pre
and post notify drivers. what exactly are the drivers expected to do with
the notification? are you asking them to pause and then re-initialize for
the new power level?
OMAP3 will require suspend to ram implementation where the content of
system memory is retained, while parts or all the SoC are switched off.
The plan is still to have a clock fw based implementation (plus
interaction with the power rails, of course).
I think these are good examples of the non-ACPI systems you are
mentioning.
yes, I think they are.
To make any proposal that has some chance of being accepted, you have to
compare it against the existing solution, explaining:
-what it is bringing in terms of new functionalities
-how it is different
it unifies all power/performance trade-offs (including power on/off) into
a single API, but decouples that API from the implementation details of
exactly what the technical details of the different modes are and how the
changes are made.
for some subsystems this would be little more then renameing existing
fucntions, for others it would be converting several indepndant functions
into one, discoverable api
-why the current implementation cannot simply be enhanced
which current implementation should be enhanced? and with the massive
broadening of functionality should it retain the same name, or should it
get renamed to something more generic?
the cpufreq implementation is very close to what I'm proposing, it would
need to get broadend to cover other devices (like disk drives, wireless
cards, etc), is this really the right thing to do or should the more
generic API go in for external use and then the existing cpufreq be called
from the set_mode() call?
You can refer to the linux-pm archives for examples of failed attempts
over the last year or so, just search for "framework" in the subject.
I'll try to do some digging.
David Lang
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